Installations of this type find widespread application in the art, with particulate materials such as catalysts and/or adsorbents. In most of the these uses, obtaining optimal performance depends on the constant thickness of each mass of particulate material in the direction of fluid flow, which is to say the geometric precision of the interface between two adjacent layers. Until now, particularly in installations with masses of concentric different adsorbents, this interfacial precision requires the emplacement, which is delicate and difficult, of an intermediate grid, as described in EP-A-0,118,349.